This invention relates to a method of preparing improved low molecular weight polycarbonamide compositions, articles prepared thereby, and to the modifier used therein. The polycarbonamides of the invention are characterized by improved impact resistance and high melt flow.
It is known that polymer modifiers can be used to improve properties of several plastic resins such as, for example, impact resistance and melt strength. U.S. Pat. Nos. 3,668,274; 3,796,771; and 3,784,497 to Owens and Clovis disclose the use of acrylic core//shell impact modifiers to impart improvement in the impact strength of higher molecularweight polycarbonamides (for example Nylons "66" and "6"), but the resulting blends do not exhibit the good flow which is necessary for injection molding operations. U.S. Pat. No. 3,963,799 to Stark-weather discloses ethylene-based rubbers as modifiers for low molecular weight easy-flow nylon, wherein caprolactam side chains are grafted onto the rubber by a specific and separate acid-amine coupling reaction. U.S. Pat. No. 3,920,602 to Freed discloses blends of nylon with a thermoplastic phenoxy resin in glass-filled systems. British Pat. No. 1,284,489 to Priddle et al. discloses ethylene-dimethylaminoethyl methacrylate copolymers as modifiers for nylon. German Pat. No. 2,356,899 to Chompff discloses cured nylon intermediates modified by butadiene-acrylic acid modifiers. U.S. Pat. No. 3,985,703 to Ferry et al. discloses a process for producing an acrylic core//shell polymer and thermoplastic polymers modified therewith. With the exception of Starkweather, the prior art is not directed to the problem of modifying low molecular weight, easy-flow nylon. Prior to the invention, core//shell polymers having high rubber core content were not capable of being admixed and dispersed in low molecular weight nylon due to the very low viscosity above the melting point and the resulting lack of shear.
It has been unexpectedly and surprisingly discovered that by obtaining an intimate dispersion of an acrylic core//shell modifier with a small amount of a higher molecular weight nylon and then blending this dispersion with a large excess of low molecular weight nylon, the impact modifier may be dispersed in the low viscosity nylon thereby yielding a final product characterized by improved impact resistance and high melt flow. By using a minimum amount of high molecular weight nylon, the melt flow of the final blend is essentially the same as that of the blend of the acrylic impact modifier and the low molecular weight nylon alone.